A device for detecting undesired arcing in electrical apparatus is disclosed in Lindgren et al's U.S. Patent Application Ser. No. 180,854 filed on Aug. 25, 1980, and assigned with the present application to a common assignee. In this known device, one or more light reflecting or light refracting members are arranged near the end of at least one optical fiber that is situated in the vicinity of a detecting unit, and the task of these members is to reflect or conduct light, caused by undesirable arcing, from locations within the electrical apparatus which lie outside the ordinary field of view of the optical fiber or fibers, which light is then conducted via the fiber(s) to measuring or indicating members at an indicating unit. The reflecting members may consist of mirrors, of parabolic, plane or other shapes, which are arranged to reflect light rays occurring within the detected space into the field of view of the optical fiber(s). The reflecting member or members may also consist of granular members or members which are fibrous on the surface, which are arranged at least partially to reflect light occurring within the detected space into the field of view of the optical fiber(s).
The primary object of the present invention is to provide an improved detecting device of the kind referred to, in which the field of view of the fiber optic means is increased compared with the known detecting device, and which constitutes a robust and reliable device for monitoring the occurrence of undesired, light-producing events.